This invention relates to layered antennas having either directional or omnidirectional field patterns in azimuth with limited elevation radiation patterns.
Conventional dipole antennas in which a pair of colinear quarter wavelength radiators are fed in anti-phase will produce a substantially omni-directional radiation pattern in a plane normal to the axis of the radiators. If the radiators are placed parallel to and a quarter of a wavelength from a reflecting ground plane the radiation pattern becomes substantially directional. If several radiators are layered vertically, the radiation pattern is substantially in azimuth and restricted in elevation. An important factor in the design of an antenna is the gain of the antenna. Provision of a reflector will increase the gain in front of the antenna while reducing the gain behind. For modern telecommunications application at high frequencies, e.g. above 100 MHz, apart from the electrical performance of the antenna other factors need to be taken into account, such as size, weight, cost and ease of construction of the antenna. Depending on the requirements an antenna can be either a single radiating element (e.g. one dipole) or an array of like radiating elements.